1. Field of the Invention
The present invention relates to an information processing device and in particular to an information processing device having a communication function.
2. Description of the Related Art
Recently, cdma2000 1×EV-DO (hereinafter referred to as EV-DO) has been developed as a next-generation high-rate radio communication system. The EV-DO is a version of specializing cdma2000 1× provided by expanding cdma2000 to the third-generation system for data communications and increasing the transmission rate. “EV” means Evolution, and “DO” means Data Only.
The EV-DO system is approximately the same as the cdma2000 1× system in the configuration of a radio interface of an upstream channel from a radio communication terminal to a base station. As for the configuration of the radio interface of a downstream channel from a base station to a radio communication terminal, whereas the bandwidth of 1.23 MHz is the same with that of the cdma2000 1× system, the modulation method and the multiplexing method are much different from those of the cdma2000 1× system. As for the modulation method, whereas QPSK and HPSK are used in the cdma2000 1× system, QPSK, 8-PSK, or 16QAM is selectively used in the EV-DO system according to a reception state of a downstream channel of a radio communication terminal. As a result, a high transmission rate with low error resistance is used when the reception state is good, and a low transmission rate with high error resistance is used when the reception state is bad.
As for the multiplexing method for enabling multiple communications from one base station to a plurality of radio communication terminals, TDMA (Time Division Multiple Access) is employed in which communications with a plurality of radio communication terminals are performed in such a manner that time is divided in units of 1/600 second, a communication is performed with one radio communication terminal in each unit time, and the radio communication terminal to be communicated is switched every unit time, rather than CDMA (Code Division Multiple Access) which is employed in the cdmaOne system and the cdma2000 1× system.
A radio communication terminal measures a carrier-to-interference power ratio (hereinafter abbreviated as CIR) of a pilot signal as an index of a reception state of a downstream channel from a base station to be communicated, predicts a reception state during the next reception time slot on the basis of a variation of the CIR, and notify “a maximum transmission rate which enables to receive with a error ratio that is lower than a predetermined rate”, which is expected from the predicted reception state to the base station as data rate control bits (hereinafter referred to as DRC) predetermined. The predetermined error rate is usually set to about 1% though it depends on the system design. The base station receives the DRCs from a plurality of radio communication terminals, and a scheduler function in the base station determines with which radio communication terminal is to communicate in each division unit time. Basically, as high a transmission rate as possible is decided on the basis of a DRC sent from each radio communication terminal and is used for a communication with it.
With the above configuration, the EV-DO system enables a maximum transmission rate of 2.4 Mbps (mega-bits per second) per sector in a downstream channel. This transmission rate is the sum of amounts of data communications from one base station to a plurality of radio communication terminals in one frequency band and in one of a plurality of sectors (usually, a plurality of sectors exist). The transmission rate increases if a plurality of frequency bands are used.
JP-A-2002-300644 is known as a related art.
A personal handyphone system, PDC, cdmaOne, CDMA2000 1×, and the like are originally intended for voice communication. In recent years, mail software, a web browser, and the like incorporated therein have made possible data communications through the Internet. Further, in the EV-DO at higher data transmission speed, importance of a data communication function is further increased, and it is assumed that a communication terminal function of PCMCIA card will be incorporated in a PC or a PDA.
Particularly, the PDA is generally small and is excellent in portability. Of course, the user can use the communication function singly with the PDA incorporating a communication function module. For example, however, when the user possesses different types of information processing devices such as a PDA incorporating a communication function and a notebook PC incorporating no communication function, if the communication function of the PDA can also be used from the notebook PC, it is convenient. In this case, the PDA incorporating the communication module requires relay means. On the other hand, while the notebook PC uses the communication function of the PDA, the function required for the PDA is only the communication function. However, since the whole PDA operates including other functions, unnecessary power consumption occurs.